1. Field of the Invention
This invention relates to a hydrocarbon (HC) adsorbing body suitable for use in an apparatus for purifying exhaust gas from an internal combustion engine in automobiles and the like.
2. Description of the Related Art
In order to purify the exhaust gas from the internal combustion engine in the automobile or the like, there are presently used pellet or monolith catalysts. The exhaust gas includes hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) as a harmful component. Particularly, the catalytic purification performance of HC is strongly influenced by the temperature of the exhaust gas, so that HC is generally purified through a noble metal catalyst at a temperature above 300.degree. C.
When the temperature of the exhaust gas is low immediately after the start of the engine, therefore, it is difficult to purify HC through the catalyst. Moreover, a large amount of HC is discharged immediately after the start of the engine and a ratio of low-temperature HC (hereinafter referred to as cold HC) occupied in the exhaust gas is large, so that it becomes serious to control the discharge of cold HC.
In order to reduce the amount of cold HC at the time of engine start, there is proposed an apparatus for the purification of exhaust gas in Japanese Patent laid open No. 2-135126.
In this apparatus, however, a carrier is coated with zeolite and then a metal is carried thereon, so that ion exchange is insufficient. Further, since Y-type zeolite or mordenite is used as the zeolite, the adsorption ability is insufficient. Moreover, the zeolite is high in the temperature dependence and preferentially adsorbs water in the exhaust gas over a temperature range from room temperature up to about 100.degree. C., so that it can not be said that the ability of adsorbing cold HC is sufficient.